One particular area in which avionics engineers have expended much effort and achieved many successes, is in the substitution of completely electro-optical systems for the conventional mechanical systems of the past. A prime example of these efforts is in the area of inertial navigation systems.
Mechanical gyroscopes have been, for years, a central component to many inertial navigation systems. Recently, the helium neon (He-Ne) ring laser gyroscope has replaced many of the mechanical gyros. However, these He-Ne ring laser gyros have disadvantages in cost and size, among others. With the recent advent of the global positioning system, which uses satellite communications to assist inertial navigation systems, the fiber optic ring laser gyroscopes are becoming more attractive.
Fiber optic ring laser gyros typically have as one of their components, an optical readout device for analyzing the frequency of light signals that are split off from the ring. Often this is done with a fiber optic directional coupler, which is connected to an optical detector by two optical fibers.
While these optical detectors have been used extensively in the past, they do have several serious drawbacks. The inclusion of the optical detectors increase the relative size, weight, part count and cost of the overall system.
Another approach to detect the rotation of a ring laser has been attempted and it is described in U.S. Pat. No. 4,431,308 entitled "Laser Angular Speed Detector Employing Non-Optical Output," which was issued to Mitsuhashi et al., on Feb. 14, 1984, which patent is incorporated herein by this reference. That design uses a laser element to detect a beat signal of the difference in frequency between a clockwise beam and a counterclockwise beam within the fiber optic ring. However, that design does not provide information on the direction of the rotation.
Consequently, a need exists for the improvement in solid state semiconductor fiber optic ring laser gyroscopes, which reduce the relative size, and weight of the gyroscopes while still providing both magnitude and direction information.